Waste slag, which an analysis shows contains heavy metals including arsenic, chromium, lead and nickel, suddenly becomes a fertilising product called Canola Plus.

Instead of being stored in heaps regulated by the Environment Protection Authority (EPA), it is ploughed into fields where cattle graze and where vegetables grow.

"Most people are probably concerned about it because of the heavy metals and stuff," Mr Ferguson said. "But it is cheaper than lime and this stuff is a hell of a lot easier to spread because it is granulated."

He first heard about the product through another farmer who had been using the material for years, apparently with great success. "You have only got to talk to people who have used it and they swear by it. But we won't use any more now until we are sure it doesn't affect things too much."

Although rebranding BHP steel waste as a fertilising product is perfectly legal, it is unknown to most consumers and even to the EPA.

When the Herald first asked BHP if it knew, the company denied all knowledge. But up to 30,000 tonnes a year isContinued Page 6